In recent years various designs of vehicle bumpers have been proposed that are intended to absorb moderate impact forces without damage to the bumper or the vehicle on which it is mounted. One approach has been to use fluid shock-absorbers mounted on the chassis of the vehicle. In the case of bumpers made of plastic, some are in the form of a molded hollow fascia with a molded plastic back-up member or bar linear welded or otherwise secured mechanically to the fascia. In some such bumpers a plastic foam member is inserted between the fascia and the back-up member, the back-up member providing a means for mounting the bumper on the frame of a vehicle. See, e.g. U.S. Pat. Nos. 3,721,433; 3,860,279; 3,866,963, 4,106,804; 4,109,951; 4,116,983; 4,134,610; 4,213,644; 4,268,079; 4,325,574; 4,328,986; 4,350,378; and 4,361,352.
While these and other types of bumpers made wholly or partially of plastic compositions do provide some degree of energy absorption, they are costly to manufacture and assemble, but, in addition, experience has shown that their ability to absorb forces encountered in a relatively moderate impact is, in many instances, insufficient to prevent damage to the bumper or the vehicle.